Colloquium – Kim Bott – Identifying sources of reflected light in unresolved exoplanet systems

Speaker: Kim Bott (SETI)

Title: Identifying sources of reflected light in unresolved exoplanet systems

Abstract: Terrestrial worlds are complex, with spatially varying surfaces and condensate distributions. While traditional studies of reflectance and transmission can provide clues about the nature of their atmospheres and surfaces, degeneracies and limitations remain. Clouds can obscure low altitude biosignatures, and high polar albedo or equatorial clouds can mimic ocean glint. Furthermore, many planetary reflectance phase curve analyses do not consider the non-Lambertian nature of the condensates and surfaces. Using polarimetry (measure of the orientation of the electric field of reflected light) and cutting-edge reflectance characterization, we seek to diminish these degeneracies, allowing for the characterization of potentially habitable worlds. In this talk I provide the context of polarimetric and reflectance characterization in my own work and more broadly. I relate this to our ongoing work to detect hot Jupiter polarized reflectance, and work providing better predictions for asymmetric phase curves from heterogeneous planets of all sizes. I share ongoing work to expand two of the most capable radiative transfer solvers in the world, to more accurately represent complex heterogeneous worlds. Validations of our polarized radiative transfer codes with Earth, Venus, and icy moon observations, show that using these new models with contemporary observational data is sensitive to biosignature gases, ocean glint, vegetation, condensate species and phase, and disk heterogeneities (polar haze/vortex, ice caps, continents, etc.). This provides a complementary means to validate habitability metrics and biosignatures, and a route to map unresolved planets in a broader array of scenarios. Predictions to aid future telescope imaging and phase curves observations show how the methods may allow us to map worlds and distinguish between condensates and surfaces. I show the steps in the path forward to mapping and more reliably characterizing exoplanets.